1. Field of the Invention
The present invention relates to methods for forming semiconductor trenches, particularly silicon trenches.
2. Description of Related Art
Highly anisotropic etching structures in silicon have many applications. For example, anisotropic trenches are required during the fabrication of semiconductor devices, such as optical biosensors, optical switches, and metal-oxide-semiconductor field effect transistor devices.
The dimensions of these trenches typically range from 1-4 μm in width and 0.5-5 μm in depth. During the fabrication of microelectromechanical systems, however, deeper anisotropic trenches are usually needed. For example, the patterning of silicon is an essential step and it may demand deep silicon trenches with depths between 10 and 100 μm. Furthermore, recently ultrathin silicon solar microcells have received increasing attention due to the reduction of material consumption. During its fabrication, pre-etching with depths of about 10 μm in the vertical direction is required for wafer slicing.
Numerous methods, including reactive ion etching (RIE), potassium hydroxide (KOH) wet chemical etching, and laser-assisted direct imprint (LADI), have been developed to fabricate silicon trenches. However, these methods have several drawbacks. RIE is a typical method for creating highly anisotropic structures in conventional semiconductor fabrication, but it utilizes expensive instruments and is rarely performed on an ultra-large scale. Moreover, an additional hard etching mask is needed for deep RIE. KOH wet chemical etching is a low cost and large-area fabrication method, but the etching direction is restricted due to the crystal orientation. LADI is a rapid etching-free technique for patterning nanostructures in silicon; however, the produced line widths and depths by LADI are limited to sub-micrometers.
Accordingly, it would be advantageous to develop a low cost and large-area method for fabricating highly anisotropic Si trenches with dimensions from nanometers to micrometers.